A heat exchanger is used in such various fields as a heater, a cooler, a evaporator, a condenser, etc. and plays a role of supplying a target fluid with some heat and taking some heat from that fluid. The former function is carried out by a heating medium and the later by a cooling medium respectively, and the heating medium and the cooling medium is said to be a heat transfer medium in a common name.
The most used one among many types of heat exchangers is the metal tube walled heat exchanger to which a watering type, a double tube type, a fin attached multi-tube type, a shell and tube type, etc., belong. A double tube type heat exchanger has an inner tube and an outer tube, of which heat exchanging takes place between the fluid at the inner tube and the fluid at a loop shaped space between the tubes, and has a very simple structure but its capacity of heat exchanging is small.
For a large capacity of heat exchanging, a shell and tube type heat exchanger of which a large outer tube has several numbers of small tube is generally used, and, besides the aforementioned heat exchanger, there are a variety of heat exchangers.
Also, as a heat exchanging medium widely used in the industries, there are water, steam, air, exhaust gas, oil, mercury, sodium, potassium, dowtherm; a mixture of specific penyl ether and specific penyl, etc.
Up to now, heat exchangers have been developed in various aspects to increase the heat transfer efficiency, and, as a heat transfer increasing method, convection increasing method by the generation of vortices of a heat transfer medium is widely used. Convection heat transfer does not take place dynamically for a laminar flow because of its poor fluid mixing effect. So, for the promotion of convection heat transfer, a method of transition of fluid into a turbulence flow by means of acceleration of fluid is used, but the acceleration of fluid is accompanied by some disadvantages that a lot of energy and excessive components are needed and noise is produced.
Recently, a method for exciting the cooling medium flowing cooling pipes in a heat exchanger was proposed. Such a example is disclosed in the published Korean patent No. 2000-21082 issued on Sep. 25, 1998: A heat exchanger and heat exchanging method using it.
This technology in the aforementioned patent discloses a method for increasing heat transfer ratio by generating the turbulent flows resulted from the excitation of the cooling medium flowing cooling pipes in a heat exchanger by means of an exciter.
With such a method, there is an advantage of more active convection heat transfer because of the removal of boundary layer, which is made up inside the cooling pipes, of a laminar flow by means of the excitation of cooling pipes. But, for this simple vibrating method does not consider the physical properties of a fluid, increasing rate is insignificant in comparison with the energy necessary for the excitation.
According to the newly published papers, it was revealed that, when a fluid flows, there are some characteristic natural frequencies. Generally, the analysis of a fluid in a specific flow field shows that there are natural instabilities in a flow pattern of a fluid. And the analysis of such a flow pattern can show some characteristic flow resonance frequencies upon the flow conditions. Also, provided with the pulses of same frequency as the characteristic flow resonance frequency of a fluid, the flow is activated to a degree of more large amplitude by means of the resonance phenomenon.
A technology to which such a phenomenon is applied is disclosed on the published Korean patent No. 2001-3358 issued on Jun. 23, 1999; A resonance cooling device of a electronic instrument. The aforementioned technology which is applied to such a large amount of heat generating electronic instrument as a computer or a communication device is used to improve the heat radiation capacity of an electronic instrument, and, for example, a method of generation of a sine wave corresponding to the natural frequency of flow inside the case of an electronic instrument is used by a sound wave generator installed therein.
In this technology, that a natural convection accompanied closed space of a computer or a communication device is supplied with a sound wave is the core technology but, in case of the real world, the flow of natural convection in a complex closed space fluctuates very randomly, the flow resonance frequency depends on the excitation conditions, and the environments work as a important factor. So, it is very difficult to detect the flow characteristic factors which affect heat transfer to a large extent and to carry out the analysis of flow resonance frequency. Accordingly, with the present know-how, there are some limitations in the application of the aforementioned technology. Also, because sound waves are only used in the excitation of a flow, it is possible to generate a resonance phenomenon in case of a heat transfer medium of the gas, especially the air only. Accordingly, A application of the corresponding technology is limited to a heat transfer medium of the gas and to cooling the components inside the case of a computer or a communication device, where natural convection takes place, and has a disadvantage of the difficulty in applying it to a heating medium of the liquid or to forced convection accompanied heat transfer medium.
Accordingly, the heat transfer technology for the application of flow resonance phenomenon demands the deep technical measures for its application to such a general field as more complex shape condition and time-variant flow condition.